The ionic conductivity of the blend is greater than one

would predict by assuming a simple linear mixing relation,

given by the dotted blue line.

1

Acknowledgments

• Simulate electrolytes with variable εAB to obtain electrolytes that are miscible/immiscible independent

of μA and Δμ• Examine the full effect of miscibility and polarity

contrast on ionic conductivity in all electrolytes

Future Work

• Salt-free blends become more immiscible with increasing Δμ

• Blend electrolytes can become more or less miscible as a function of both μA and Δμ

• Ionic conductivities negatively deviate or follow a linear mixing relation, seemingly independent blend

electrolyte miscibility

Conclusions

This authors thank the Robert A. Welch Foundation (Grant nos. F-1599 and F-1904) and the National Science Foundation (DMR-1306844, CBET-17069698) for financial support for this work, the Texas Advanced Computing Center for

access to high-performance supercomputers.

Miscibility and Ion Transport in Blend Polymer Electrolytes

Bill K. Wheatle, Nathaniel A. Lynd, Venkat Ganesan

Model

Propylene carbonate (PC) Dimethoxyethane (DME)

High mobilityHigh polarity

In common lithium-ion battery electrolytes, blends of liquid solvents containing some high polarity component

and some high mobility component is common.

Can we achieve similar behavior in blends of polymersserving as hosts for salt, particularly in the case of

polymers with significant polarity and mobility contrast?

Introduction

References1. Xu, K. Chem. Rev. 2004, 104 (10), 4303–4417.

2. Wheatle, B. K. et al. ACS Macro Lett. 2018, 1149–1154.3. Liu, L.; Nakamura, I. J. Phys. Chem. B 2017, acs.jpcb.7b00671.

4. Sorte, E. G. et al. Macromolecules 2018.

We seek to answer two questions: (1) what role does polarity and mobility contrast play in blend polymer

electrolytes play and (2) how does the miscibility of a blend electrolyte influence ionic transport?

We will vary the dipole strength of the low polarity host (μA), the dipole contrast between low and high polarity

hosts (Δμ=μB-μA), the Lennard-Jones interaction strength between low and high polarity hosts (εAB) to control polarity contrast and electrolyte miscibility within a

coarse-grained molecular dynamics framework.

• A freely rotating, point dipole embedded in each

monomer (μ)• Lennard-Jones hard-core

repulsion (ε)Stockmayer Polymer Model

2,3

ResultsQuantifying miscibility via the structure factor:

where gAB(r) is the radial distribution function between monomers of type A and B and xi is the mole fraction of species i. This measures the

spatial correlations between low and high polarity polymers.

Effect of polarity contrast (Δμ) on blend miscibility

We simulated salt-free 50:50 m:m blends to understand the behavior of S12(q) upon phase separation. Regularly spaced peaks form in blends

with the largest Δμ, which we interpret to correspond to immiscibility.

Snapshots corresponding to blends with μA = 1.0 μEO. Note phase

separation only in largest Δμ blend.

Δμ= 0.1 μEO

Δμ= 0.4 μEO

Δμ= 0.8 μEO

We first simulated 50:50 mA:mB blends with [salt] = 16 [cations]/[monomer] to understand the effect of salt on miscibility.

Effect of addition of salt on blend miscibility

• Addition of salt decompatibilizes(peaks appear) blends with Δμ = 0.4 μEO, but the effect is lessened with increasing μA

• Contrariwise, salt compatibilizes(decreases peak height) blends with Δμ = 0.8, but the effect increases with increasing μA

Results Cont’dIonic conductivity measurements

4

• Hollow: immiscible• Filled: miscible

• Conductivities seem to follow linear mixing or negatively

deviate, regardless of miscibility